Alkaline dry cell



b. Z0, 953 s. RUBEN 2,542,739

ALKALINE DRY CELL Filed Oct. l5, 1946 :Ji-33 lL-g- NX@ 40 39 aNvEN-ron54 44 .Samui Euhm 30 ,SILVER Harm [aP/fn M4 f Patented ret. 2o, 1951+-samuel Ruben, New michelle,y QY.

Application october 151946, swarm. 703,386

. l .This invention relates t alkaline dry cells.

This application ls a continuation-in-part of 'co-pending applicationsSerial No. 486,367, filed May 10, 1943, now a Patent #2,481,539, issuedDecember 16, 1948, Serial No. 604,269, led July 10,1945,` now Patent No.2,422,045; and Serial No. 671,200, filed May 2l, 1946, by Samuel Buben.f

An object of the invention is to improve alka line primary cells.

Another object is to produce an alkaline dry cell having a silver oxideelectrode.

Features of the present invention reside in the use of a coherentconductive electrode comprising compressed or bonded silver oxide powderin an alkaline primary cell and in the means for preparing and improvingthe properties of such a cell. In the preferred embodiments the anode isof amalgamated zinc, the cathode of silver oxide and the electrolyte ofpotassium hydroxide solution containing potassium zincate.

In the drawings:

Figure 1 is a top view of an alkaline dry cell embodying features of thepresent inventin;

Figure 2 is a section on the line 2--2 of Figure 1;

Figure 3 is a section through a modified dry cell; and

Figure 4 is a perspective view of a modiiied spacer element for the cellof Figure 3.

Referring to Figures 1 and 2 the cell is enclosed in a steel can 9 theinside surface of which is coated with a thin silver layer i0,preferably applied rby electroplating. The depolarizing electrode orcathode il is formed of silver oxide powder which is pressed into thebottom of the container to form a compressed coherent cathode layer indirect contact with the silver plate. Finely-divided silver oxide (AgzO)powder is preferred without the admixture of other ingredients. Theother oxides of silver, such as the peroxide (AgO) can also be used. Thesilver oxide powder is compressed in the bottom of can 9 underrelatively high pressure, such as 30,000 pounds per square inch.

A barrier layer i2, comprising a disc of a minutely-porous electrolytepermeable material such as an organic film or libre sheet or a presseddisc of powdered organic or inorganic material which is substantiallyinert to the cell electrolyte is placed over the cathode layer. Suitablematerials are pressed polystyrene bre, nylon fibre,

pressed powders of polystyrene, pressed discs of v magnesium silicate ormagnesium hydroxide powder, pressed ceramic or glass powder, or puriedsheet asbestos. l Glycerine plasticized hns 13 claims. icl. 1st-107)'.

of polyvinylalcohol aswell as parchment paperof dialysis grade landregenerated sheet cellulose may also be used. Thebarrier preventsmigration of impurities and silver compounds from the cathode to theanode. ln some cases, especially where silver oxide of highpurity isused, the bar- '-rier may be eliminated. l

The anode-spacer assembly for the cell is formed by windingup a strip ofcorrugated zinc foil i3 withinterleaved porous paper strips 'I4 inoifset relation so that the edge of the foil projects slightly from oneend of the roll and the edge of the paper projects at the other end ofthe roll. One or two layers of a pure wood cellulose nbre paper, such asfilter paper or Dexter paper, or of a cotton fibre paper such as Feltrilpaper are suitable for the paper spacer I4. The paper strips` are longerthan the zinc strip and overlap it on the outside of the roll by one ortwo turns. The roll is inserted in an impervious insulating sleeve il,of an alkali resistant plastic, such as polystyrene, polyethylene,neoprene, or ethyl cellulose.

The cell electrolyte preferably is formed of an aqueous solution ofpotassium hydroxide containing a substantial quantity of potassiumzincate. The preferred range of concentration of the potassium hydroxideused in preparing the electrolyte for a cell of the construction shownin Figure 1 and most other cell structures is from thirty to fty percent (30 to 50%) KOH. Concentrations above and below these limits can beused but generally result in lower cell output emciencies. However, thisdepends considerably upon the cell construction and conditions of useand it is feasible with certain of the structures illustrated to depart.rather widely from the preferred range, even to the extent of usingsuch a high concentration of KOH as to produce an electrolyte which issolid at normal temperatures.

For minimum attack on the amalgamated zinc anode by the electrolyte whenthe cell is standing on open circuit, the electrolyte should contain allthe zinc it will take up at the temperatures to which the cell is to besubjected. However, I have found that proportions of zincate down toabout one-half this optimum concentration will, in many cases,particularly for moderate temperature uses, produce only minute gasgeneration, the rate being sufficiently slow to permit generated gas todiuse out of the cell through the grommet or other sealing means withoutdeleterlously aiecting the desired airtight enclosure of internal cellelements. The quantity of zinc which will dissolve in the electrolyteappears to be proportional to the alkali concentration. It is j2,542,7"10 yI' 1 apparent that `the reaction f zinc or zinc oxide withthe potassium Yhydroxide in preparing the electrolyte will convert partvoi' the hydroxide/to potassium zincate. The best range for'electrolytes made from thirty to fty per cent (30' to 50%) KOH solutionis about liitteen to' 1o seventeen grams to 17 grams) of zinc per onehundred grams`(100 gms.) of KOH used.

I have made a satisfactory electrolyte for cells of the type shown inFigure 1 by adding seventyiive grams (75 gms.) of C. P. potassiumhydroxide 15 (containing 88% KOH) to twenty-five milliliters ml.) ofwater, adding twelve grams (l2 gms.) of zinc oxide, stirring and heatingto one hundred eighty to one hundred ninety degrees centigrade (ISO-190C.). The solution was thenl 2o allowed to cool to one hundred tendegrees centigrade (110 C.), after which twenty-live milliliters (25ml.) of water was added and the solution stirred and cooled to eightydegrees centigrade (80 0.). An additional fty milliliters 25 (50 ml.) ofwater was added and a clear solution was obtained. Made in this way theelectrolyte does not precipitate any zinc: oxide when cooled to roomtemperature. This solution appears to be about seventy-five per cent(75%) saturated 30 with zinc at room temperature.

In cases where the volume of electrolyte is relatively small a moreconcentrated electrolyte may be used in order to have sufficientelectrolyte capacity to utilize all the zinc and depolarizer.- Anelectrolyte containing one hundred gramsf (100g.) of C. P. potassiumhydroxide to one hundred milliliters (100 ml.) of water and sixteengrams (16 g.) of zinc oxide, made by asimilar method, has been used insome cells of small dimensions. It requires a minimum of about 0.22 gramof this electrolyte per gram of AgaO depolarizer for completeutilization of the electrodes. With lower KOH concentrations a largeramount of'electrolyte is required. i

Since amalgamated zinc foil is too brittleV to wind into a roll theamalgamation of roll I3 is performed after winding. The roll is ilrstimpregnated with electrolyte which causes the spacer I4 to swell intothe space afforded by the corrugations in the zinc foil. A measuredquantity of mercury is distributed on top of the roll in contact withthe zinc and is determined by calculation or experiment. Desirableproportions of mercury are ve to twenty per cent (5 to 20%) of theweight of the zinc. The roll is then placed on a porous suction platewhich draws the mercury into the roll and removes excess electrolyte.The electrolyte proinotes spreading of the mercury so that the entirezinc surface becomes amalgamated in a short time.

Inassembling'the cell the barrier layer I2 is placed over the surface ofthe cathode and the electrolyte-impregnated anode rollis placed in thecontainer with the projecting paper end in contact with the barrier.Electrolyte from the anode roll readily impregnates the barrier layerand wets the top face of the cathode.

Plastic grommet I6 is tted over the edge of top disc I5 and the disc isthen placed with its inner face in contact with the projecting edge ofzinc foil anode I3. Container I0 is provided with a shoulder I8 uponwhich the grommet rests. The free edge I9 of container 9 is then turnedor spun in over the grommet to apply pressure thereneoprenastyraloy(polystyrene and butadiene plastic), poiyethyiene or the nke. 'f i,

The top disc I5 which forms a,terminal zinc anode and also comprises an.enclosing wall and seal the assembly and produce anali'-A 'tight cell.Grommet Il is formed of a, -non-rigid alkali resistant plasticmaterialsuch as rubber,

for the cell'is formedof copper or oflsilv'er, coated 4 copper. Copperalloys having a, low polarization potential difference to zinc in thealkaline electrolyte are also suitablefsuch as copper-cadmium alloys andcopper-zinc alloys having not more than 4 10% o! zinc. The copper maybeusedu'n-4 coated, or mercury amalgamated, but it is pre.-

ferred to plate lthe xsurface'oi? the disc with silver. The silverrenders the surface' more rapidly;l

I amalgamable andl provides anl improvedl lowre-l sistance contact withthe amalgamated zinc anode inside the cell and `with externalscircuitconnections outside the cell.

Copper top discs I5 can be readily coated with a.- rm thin silvercoating by a contact galvaxilcA i process which consists in tumblingtheldiscs in A the following solution for iive minutes: v

Potassium cyanide Vgrams `:20

Silver chloride do (i-` Potassium hydroxide do 2 L. Water liters-- Uponremoval from the solution, washing and drying, the discs are ready foruse. The discs can also be coated with silverfby electroplating.

The inner silver or copper surface of the top disc becomes amalgamatedby contact with the amalgamated zinc anode thereby forming an amalgam`ioint or bond with the anode when the cell is assembled.

By way of example, one cell having the construction shown in Figure 1with a cathode of silver oxide pressed to a density o! 5.4 had adiameter of inch and was inch high. The zinc anode formed 01.5 mil zincfoil corrugated with 2 mil deep corrugations, the corrugated foil stripbeing 0.25 inch wide and 22 inches long. The foil was wound up with two4 mil porous paper spacers 0.34 inch wide. The zinc projected 10 mils atthe top of the roll and the paper a, of

7an inch at the bottom. The barrier consistedof one disc of dialysispaper 3 mils thick.

Figure 3 is a sectional view of a at primary cell having a silver oxidecathode 3|, an alkaline gell electrolyte 33 and an anode 32 of amalgamated zinc powder or shot.

Anode 32 may be a porouspressed coherent body of amalgamated zinc shotor powder of graduated sizes, all-ot which will pass through a 28-meshscreen. The shot or powder may be amalgamated with 15% of mercury undera 15% ammonium hydroxide solution. The mixture of zinc shot or powderand mercury is stirred or tumbled in a bottle until the mercury is welldistributed, after which the shot or powder is washed with water, vacuumdried at C. and pressed into the anode cup 30.

Anode cup 30, comprising one of the enclosing walls of the cell is ashallow cup having an outwardly ared ange 4I at its edge and .ispreferably formed of copper which is coated inside and outside with asilver coating and amalgamated on the inside. Amalgamated copper withoutsilver coating is also satisfactory for the anode cup.

Electrolyte layer 33 is a self-supporti. g disc formed of an aqueousalkali solution immobilized as a gel. The preferred electrolyte isformed of:

C. P. potassium hydroxide (88% This electrolyte when made as previouslydescribed is immobilized with 6 grams of sodium carboxymethylcelluloseper 100 millilitres of the alkali zincate solution. In making theelectrolyte the potassium hydroxide is added to millilitres of water andthe zinc oxide added. The mixture is stirred and heated to 180-190 C.and then allowed toncool at 110 C., after which 25 ml. of water is addedand the solution stirred and cooled at 80 C. The remaining 50 ml. ofwater is added, a clear solution being obtained. The sodiumcarboxymcthylcellulose is crushed and screened through a 40 mesh screenand is added slowly to the solution, with constant stirring. Thisdispersion is heated to slightly below the boiling point of the mixture(11'7 to 120 C.), at which point a clear liquid solution is obtained.This solution is poured into a fiat mold and allowed to cool andsolidify, after which it is removed as an elastic or resilient sheet anddiscs 33 are punched from it.

A molded grommet 39 of a non-rigid, alkaliresistant plastic materialsuch as rubber, neoprene, polyethylene, Styraloy (polystyrene andbutadiene plastic) or the like is fitted over the ilange 4| of cup 30.

The silver oxide cathode member 3| is compressed in the bottom of ashallow steel or iron cup 35 having a silver layer 36 covering itsinside surface. ange having a fiat circular portion 31 and a cylindricalportion 38 capable of fitting over the outer periphery of grornmet 39.The silver oxide layer 3| is pressed into cup 35 to the level of flangeportion 3l. In assembling the cell the electrolyte disc is laid on theanode layer, the cathode member is placed down over theanode-electrolyte assembly and the edge 40 of the cathode container isspun in to compress the grommet and seal the cell.

The spacing between anode and cathode is less than the originalthickness of electrolyte gel disc 33 with the result that the gel discis compressed when the cell is assembled and its diameter expanded tosubstantially completely iill any free space around the outer edge ofthe cell, as indicated at 44. The gel retains some or all of itsresiliency or tendency to return to its original shape thereby applyingpressure against both anode and cathode.

One practical cell having the construction shown in Figure 3 employed acopper anode cup drawn from 20-mil sheet copper and a steel cathode cup35 drawn from 15-mil sheet steel. For the cathode 8.5 grams ofgranulated silver oxide which had been pelleted at 10,000 pounds persquare inch was consolidated in the steel cup at 30,000 p. s. i. to athickness of 105 mils.

The anode comprising 3.54 grams of amalgamated zinc powder containing15% mercury was pelleted at 5,000 p. s. i. to a disc 1.065 inches indiameter and then consolidated into the silver coated copper containerat 15,000 p. s. i. to a thickness of 38 mils.

The electrolyte disc 33 (of potassium hydroxide and potassium zincategel) was a 180 mil thick molded gel disc .935 inch in diameter andweighing 3.06 grams. Since the spacing between the The edge of cup 35 isformed with a anode and cathode in the assembled cell was about mils itis apparent that the gel disc was substantially compressed and expandedin diameter upon assembly.

A smaller cell of similar construction contained 1.125 grams of thedepolarizer and .468 gram of the amalgamated zinc powder.

Figure 4is a perspective view of a modified electrolyte-spacer element43 for use in the cell of Figure 3, in place of element 33. Element 43comprises a disc of porous absorbent sheet material impregnated with theelectrolyte, which may be either the gel or the liquid previouslydescribed. The preferred absorbent material is a pure felted cottoniibre paper, such as Feltril paper, about 60 mils thick. v

Where the volume of liquid or gel electrolyte is small it may bedesirable to pre-impregnate the cathode 3| with liquid electrolytebefore assembly to displace air and afford better electrolyte contact.

Other gelling agents which can be used for the electrolyte are starchand methyl cellulose.A

According to a feature of the present invention the initial conductivityof the cell is improved by an aging procedure. This comprises drawing asmall electric current from the cell for a preliminary aging period,before the cell is put into use. This reduces a small amount of thesilver oxide to metallic silver. The reduction under these conditionsappears to proceed in such a manner that tiny threads or stringers ofmetallic silver grow throughout the oxide layer from theelectrolyte-engaging surface of the cathode terminal element or wall,such as the bottom of the silverplated steel cup. These are shown at 22and 42 in Figures 2 and 3 respectively.

'Ihe silver plating of the steel or other metal of the cathode terminalor container provides good electrical contact with the silver oxide anda contact in which a potential difference or p0- larized layer `cannotdevelop.

While steel or iron is the preferred material for the cathode containeror terminal, because of its relative inertness, strength and economy,other metals can be used as a base for the silver deposit, such asnickel or nickel alloys.

As is pointed out in application Serial No. 604,- 269, the amalgamatedzinc anode should have a large surface area, preferably at least equalto 20 square inches per gram of oxygen available from the depolarizer.

From the overall cell equation:

it is apparent that one mol of silver oxide is reduced to silver foreach gram atomic weight of zinc consumed at the anode. It is thereforeapparent that ii 100% utilization of materials is ,obtained anelectrochemical balance between zinc and silver oxide will be present ifthese materials are used in the ratio of the atomic weight of zinc tothe molecular weight of silver oxide, namely if the weight of zinc is0.354 of the weight of silver oxide in the cell.

Using zinc amalgam containing 15% of mercury and a silver oxidedepolarizer a balance is obtained with 0.416 gram of amalgam per gram ofdepolarizer.

It is apparent from the foregoing description that the novel primarycell combination described provides a leakproof dry cell which remainssealed during shelf life, during use and after end of life. This is madepossible by the balance of materials of anode and cathode, the provisionof 7" i inert cell enclosing walls, and the use of an alkalineelectrolyte which does not react with either electrode to generatesubstantial gas at any time.

What is claimed is:

1. An alkaline dry-cell comprising, in combination, a coherentconductive cathode comprising an oxide of silver, an anode ofamalgamated zinc, an immobilized alkaline electrolyte,`and a terminalfor said cathode having at least the surface in contact with saidcathode formed of metallic silver, said cell being characterized by theabsence of free liquid electrolyte.

2. An alkaline dry cell comprising, in combination, a steel cup havingthe inside surface thereof coated with silver. an electrode layer ofsilver oxide compressed in the bottom thereof in contact with saidsilver coating, an immobilized body of alkaline electrolyte in contactwith the surface of said oxide layer, an amalgamated zinc electrode incontact with said electrolyte, and a closure for said cell in contactwith said zinc electrode comprising a metal wall having at least thesurface in contact with said zinc electrode constituted by amalgamatedmetal selected from the group consisting of copper and silver forming anamalgam bond with the zinc electrode.

3. An alkaline drycell comprising, in combination, a steel cup having asilver coating on the inside bottom and side wall thereof, a coherentcathode of silver oxide powder compressed in the bottom thereof incontact with said silver coating, an immobilized body of aqueouspotassium hydroxide solution containing a substantial quantity ofpotassium zincate in contact with the surface of said cathode. anamalgamated zinc anode of large surface area in contact with saidelectrolyte, a terminal in contact with said anode. said terminal havingat least the surface in contact with said anode constituted byarnalgamated metal selected from the group consisting of copper andsilver forming an amalgam bond with said anode, and an insulatingsealing member insulating said terminal from said cup and sealing saidcell.

4. An alkaline dry cell comprising, in combination, a rst copperterminal having a silver coating thereon, a coherent conductiveelectrode comprising silver oxide in Contact with said silver coating,an immobilized body of alkaline electrolyte in contact with the surfaceof said electrode, an amalgamated zinc electrode in contact with saidelectrolyte, and a second copper terminal in contact with saidamalgamated zinc electrode, said second terminal being amalgamated andforming an amalgam bond with said zinc electrode, said cell beingcharacterized by the absence of free liquid electrolyte.

5. An alkaline dry cell comprising, in combination, an airtightenclosure comprising a rst and a second terminal and insulating sealingmeans therebetween, the first said terminal having at least its innersurface formed of silver, the second of said terminals having at leastits inner surface formed of amalgamated metal selected from the groupconsisting of copper and silver, a coherent conductive cathodecomprising silver oxide in contact with the silver surface of said rstterminal, an amalgamated zinc anode in contact with the amalgamatedsurface of said second terminal and forming an amalgam bond therewith,and an immobilized body of aqueous alkali metal hydroxide electrolytebetween and in contact with said anode and cathode, said electrolyteinitially containing a substantial lio ' 8 quantity of alkali metalzincate to reduce local chemical attack of said electrolyte on saidanode and limit gas generation within said cell, said cell beingcharacterized by the absenhce of free liquid electrolyte.

6. An alkaline dry cell comprising, in combination, a conductiveterminal, a compressed coherent body of silver oxide powder in contacttherewith, a body of alkaline electrolyte in contact with the surfaceAof said powder body, and an amalgamated zinc electrode in contact withsaid electrolyte, said silver oxide body having portions thereof reducedto provide stringers of metallic silver throughout the thickness of saidbody.

7. An alkaline dry cell comprising, in combination, an anode comprisinga body of amalgamated zinc, a coherent conductive cathode comprising anoxygen-yielding compound, said cathode being spaced from said anode, acell enclosure enclosing said anode and cathode and having conductiveterminals in contact with vsaid anode and cathode respectively, and anelectrolyte body within said enclosure and held thereby undercompression in contact with said anode and cathode, said electrolytebeing a self-supporting resilient alkaline gel comprising thevheatreaction product of an aqueous solution of potassium hydroxide,potassium zincate and sodium carboxymethylcellulose.

8. A dry cell comprising an anode and a cathode in spaced relation, andan electrolyte body therebetween, said electrolyte body comprising aselfsustaining elastic gel which will progressively shrink duringdischarge of the cell, the spacing between said anode and cathode beingless than the original thickness of the electrolyte body by an amountgreater than the maximum shrinkage of said body whereby the electrolytebbdy will be held under compression between and in intimate contact withsaid anode and cathode throughout the useful life of the cell.

9. A dry cell comprising an anode and a cathode in spaced parallelrelation, a layer of electrolyte between said anode and cathode and incontact therewith, said electrolyte layer comprising an elastic gelsheet which will progressively shrink during discharge of the cell, andclamping means applying pressure to said anode, cathode and electrolyte,the spacing between said anode and cathode being less than the originalthickness of the electrolyte layer by an amount greater than the maximumshrinkage of said layer whereby the electrolyte layer will be held undercompression between and in intimate contact with said anode and cathodethroughout the useful life of the cell.

10. An alkaline dry cell comprising, in combination, an anode comprisinga layer of amalgamated zinc, a coherent conductive cathode layer inspaced parallel relation to said anode, said cathode comprising anoxygen-yielding compound, a layer of electrolyte between said anode andcathode and in contact therewith, said electrolyte comprising aresilient alkaline gel sheet which will progressively shrink duringdischarge of the cell, and clamping means applying pressure to saidanode, cathode and electrolyte layers. the spacing between said anodeand cathode layers being less than the original thickness of saidelectrolyte layer by an amount greater than the maximum shrinkage ofsaid layer whereby the electrolyte layer will be held under compressionbetween and in intimate contact with said anode and cathode layersthroughout the useful life of said cell.

11. An alkaline dry cell comprising, in combination, an anodecomprisinga body of amalgamated zinc, a coherent conductive cathode comprising anoxygen-yielding compound, saidv cathode being spaced from said anode, acell enclosure enclosing said anode and cathode having conductiveterminals in contact with said anode and cathode respectively, and anelectrolyte body within said enclosure between said anode and cathode,said electrolyte body being formed of a resilient alkaline gelcomprising an aqueous solution of potassium hydroxide and a gellingagent therefor which will progressively shrink during discharge of thecell, the spacing between said anode and cathode being less than theoriginal thickness of said resilient electrolyte body by an amountgreater than the maximum shrinkage of said body whereby said body willbe maintained under compression and in intimate contact with saidcathode and anode throughout the useful life of the cell.

12. An alkaline dry cell comprising, in combination, an amalgamated zincanode and a coherent conductive cathode comprising an oxide of silver inspaced relation, and an electrolyte body therebetween. said electrolytebody comprising a self-sustaining elastic gel which will progressivelyshrink during discharge of the cell, the spacing 'between saidy anodeand cathode being less than`\the original thickness of the electrolytebody by an amount greater than the maximum shrinkage of said bodywhereby said body will be held under compression between and in intimatecontact with said anode and cathode throughout the useful life of thecell.

13. An alkaline dry cell comprising, in combination, an anode comprisinga body of amalgamated zinc, a coherent conductive cathode REFERENCESCITED Y The following references are of record in the ille of thispatent:

UNITED STATES PATENTS Number Name Date 403,451 Barrett May 14, 1889753,138 Hubbell Feb. 23, 1904 827,861 Gardiner Aug. 7, 1906 940,043Morrison Nov. 16, 1909 1,137,226 Manchester Apr. 27, 1915 2,317,711Andre Apr. 27, 1943 2,422,045 Ruben June 10, 1947 FOREIGN PATENTS NumberCountry Date 16,471 Great Britain 1915 OTHER REFERENCES Ser. No.394,417, Marhenkel (A. P. C.), published.y May 11, 1943.

Hollabaugh et al., J. Ind.` and Eng. Chem., October, 1945, page 943.

Trans. Electrochemical Society. vol. 90 (1946), pages 398.5399, 424,425, 468, 469.

1. AN ALKALINE DRY CELL COMPRISING, IN COMBINATION, A COHERENTCONDUCTIVE CATHODE COMPRISING AN OXIDE OF SILVER, AN ANODE OFAMALGAMATED ZINC, AN IMMOBILIZED ALKALINE ELECTROLYTE, AND A TERMINALFOR SAID CATHODE HAVING AT LEAT THE SURFACE IN CONTACT WITH SAID CATHODEFORMED OF